A pillow is an essential part of healthy sleep. By “pillow”, we mean a support for the head, usable while sleeping in a bed. In most cases, pillows are cushioned, i.e. padded and therefore compliant to some degree, with a varying degree of softness, but this is not universally the case.
Internally, most pillows comprise a filler made from foam, synthetic fills, feathers, down, buckwheat (and polymeric imitations), cotton, air, or a suitable fluid. The fill is surrounded with a cover or shell made of cloth or silk, known as the pillow case or pillow slip.
Pillows can be used to provide support for the head while sleeping, to prevent the head from drooping. If such support is not provided, then neck and head discomfort can result and sleep can be disturbed. Both will have undesirable effects on the sufferer.